Magnetic nanoparticles are particles composed of ferrite (e.g., Fe3O4 and Fe2O3) and have been suggested for use in delivering drugs or physiologically active materials with or without coatings such as dextran, lipid, liposome, polymer or the like (JP 2002-128523; JP 9-110722; U.S. Pat. No. 7,560,097; U.S. Pat. No. 7,731,648). However, the use of magnetic nanoparticles in the medical field relies on maintaining a physiologically active material within the nanoparticles and selective delivery to an intended site (targeting capability).